A recent report described two affected siblings presenting osteopetrosis associated with severe combined immunodeficiency (SCID) caused by a large deletion on chromosome 11 encompassing RAG1 and RAG2 genes and the 5′ region of TRAF6 (TNF receptor-associated factor 6 gene), the most important adaptor for the RANK/RANKL signaling pathway (57). The gene discussed is TNFSF11; the disease is osteopetrosis.